This work is licensed under a Creative Commons Attribution 2.5 License.

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     -  modification, are permitted provided that the following conditions
     -  are met:
     -  1. Redistributions of source code must retain the above copyright
     -     notice, this list of conditions and the following disclaimer.
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     -     disclaimer in the documentation and/or other materials
     -     provided with the distribution.
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    README (version 1.84.0)
    File update: 23 Dec 2023
    ---------------------------

    gunzip leptonica-1.84.0.tar.gz
    tar -xvf leptonica-1.84.0.tar

Building leptonica
I/O libraries leptonica is dependent on
Generating documentation using doxygen
Developing with leptonica
What's in leptonica?

## Building leptonica

    1. Top view

      This tar includes:
        (1) src: library source and function prototypes for building liblept
        (2) prog: source for regression test, usage example programs, and
            sample images
      for building on these platforms:
         -  Linux on x86 (i386) and AMD 64 (x64)
         -  OSX (both powerPC and x86).
         -  Cygwin, msys and mingw on x86
      There is an additional zip file for building with MS Visual Studio.

      Libraries, executables and prototypes are easily made, as described below.

      When you extract from the archive, all files are put in a
      subdirectory 'leptonica-1.84.0'.  In that directory you will
      find a src directory containing the source files for the library,
      and a prog directory containing source files for various
      testing and example programs.

    2. Building on Linux/Unix/MacOS

      The software can be downloaded from either a release tar file or
      from the current head of the source.  For the latter, go to a directory
      and clone the tree into it (note the '.' at the end):
         cd [some directory]
         git clone https://github.com/DanBloomberg/leptonica.git .

      There are three ways to build the library:

        (1) By customization:  Use the existing static makefile,
            src/makefile.static and customize the build by setting flags
            in src/environ.h.  See details below.
            Note: if you are going to develop with leptonica, the static
            makefiles are useful.

        (2) Using autoconf (supported by James Le Cuirot).
            Run ./configure in this directory to
            build Makefiles here and in src.  Autoconf handles the
            following automatically:
                * architecture endianness
                * enabling Leptonica I/O image read/write functions that
                  depend on external libraries (if the libraries exist)
                * enabling functions for redirecting formatted image stream
                  I/O to memory (on Linux only)
            After running ./configure: make; make install.  There's also
            a 'make check' for testing.

        (3) Using cmake (supported by Egor Pugin).
            The build must always be in a different directory from the root
            of the source (here).  It is common to build in a subdirectory
            of the root.  From the root directory, do this:
                mkdir build
                cd build
              Then to make only the library:
                cmake ..
                make
              To make both the library and the programs:
                cmake .. -DBUILD_PROG=1
                make
            To clean out the current build, just remove everything in
            the build subdirectory.

      In more detail for these three methods:

        (1) Customization using the static makefiles:

           * FIRST THING: Run make-for-local.  This simply renames
                   src/makefile.static  -->  src/makefile
                   prog/makefile.static -->  prog/makefile
             [Note: the autoconf build will not work if you have any files
              named "makefile" in src or prog.  If you've already run
              make-for-local and renamed the static makefiles, and you then
              want to build with autoconf, run make-for-auto to rename them
              back to makefile.static.]

           * You can customize for:
             (a) Including Leptonica image I/O functions that depend on external
                 libraries, such as libpng.  Use environment variables in
                 src/environ.h, such as HAVE_LIBPNG.
             (b) Disabling the GNU functions for redirecting formatted stream I/O
                 to memory.  By default, HAVE_FMEMOPEN is enabled in src/environ.h.
             (c) Using special memory allocators (see src/environ.h).
             (d) Changing compile and runtime defaults for messages to stderr.
                 The default in src/environ.h is to output info, warning and
                 error messages.
             (e) Specifying the location of the object code.  By default it
                 goes into a tree whose root is also the parent of the src
                 and prog directories.  This can be changed using the
                 ROOT_DIR variable in makefile.

           * Build the library:
             - To make an optimized version of the library (in src):
                   make
             - To make a debug version of the library (in src):
                   make DEBUG=yes debug
             - To make a shared library version (in src):
                   make SHARED=yes shared
             - To make the prototype extraction program (in src):
                   make   (to make the library first)
                   make xtractprotos

           * To use shared libraries, you need to include the location of
             the shared libraries in your LD_LIBRARY_PATH.  For example,
             after you have built programs with 'make SHARED=yes' in the
             prog directory, you need to tell the programs where the shared
             libraries are:
                 export LD_LIBRARY_PATH=../lib/shared:$LD_LIBRARY_PATH

           * Make the programs in prog/ (after you have make liblept):
             - Customize the makefile by setting ALL_LIBS to link the
               external image I/O libraries.  By default, ALL_LIBS assumes that
               libtiff, libjpeg and libpng are available.
             - To make an optimized version of all programs (in prog):
                   make
             - To make a debug version of all programs (in prog):
                   make DEBUG=yes
             - To make a shared library version of all programs (in prog):
                   make SHARED=yes
             - To run the programs, be sure to set
                 export LD_LIBRARY_PATH=../lib/shared:$LD_LIBRARY_PATH

        (2) Building using autoconf  (Thanks to James Le Cuirot)

           * If you downloaded from a release tar, it will be "configure ready".
           * If you cloned from the git master tree, you need to make the
             configure executable.  To do this, run
                autogen.sh.

           Use the standard incantation, in the root directory (the
           directory with configure):
              ./configure    [build the Makefile]
              make   [builds the library and shared library versions of
                      all the progs]
              make install  [as root; this puts liblept.a into /usr/local/lib/
                             and 13 of the progs into /usr/local/bin/ ]
              make [-j2] check  [runs the alltests_reg set of regression tests.
                                 This works even if you build in a different
                                 place from the distribution. The -j parameter
                                 should not exceed half the number of cores.
                         NOTE: If the test fails, it's likely due to a race
                               condition.  Rerun with 'make check']

           Configure supports installing in a local directory (e.g., one that
           doesn't require root access).  For example, to install in $HOME/local,
               ./configure --prefix=$HOME/local/
               make install
           For different ways to build and link leptonica with tesseract, see
               https://github.com/tesseract-ocr/tesseract/wiki/Compiling
           In brief, using autotools to build tesseract and then install it
           in $HOME/local (after installing leptonica there), do the
           following from your tesseract root source directory:
                ./autogen.sh
                LIBLEPT_HEADERSDIR=$HOME/local/include ./configure \
                   --prefix=$HOME/local/ --with-extra-libraries=$HOME/local/lib
                make install

           Configure also supports building in a separate directory from the
           source.  Run "/(path-to)/leptonica-1.84.0/configure" and then "make"
           from the desired build directory.

           Configure has a number of useful options; run "configure --help" for
           details.  If you're not planning to modify the library, adding the
           "--disable-dependency-tracking" option will speed up the build.  By
           default, both static and shared versions of the library are built.  Add
           the "--disable-shared" or "--disable-static" option if one or the other
           isn't needed.  To skip building the programs, use "--disable-programs".

           By default, the library is built with debugging symbols.  If you do not
           want these, use "CFLAGS=-O2 ./configure" to eliminate symbols for
           subsequent compilations, or "make CFLAGS=-O2" to override the default
           for compilation only.  Another option is to use the 'install-strip'
           target (i.e., "make install-strip") to remove the debugging symbols
           when the library is installed.

           Finally, if you find that the installed programs are unable to link
           at runtime to the installed library, which is in /usr/local/lib,
           try to run configure in this way:
               LDFLAGS="-Wl,-rpath -Wl,/usr/local/lib" ./configure
           which causes the compiler to pass those options through to the linker.

           For the Debian distribution, out of all the programs in the prog
           directory, we only build a small subset of general purpose
           utility programs.  This subset is the same set of programs that
           'make install' puts into /usr/local/bin.  It has no dependency on
           the image files that are bundled in the prog directory for testing.

        (3) Using cmake

           The usual method is to build in a directory that is a subdirectory
           of the root.  First do this from the root directory:
                mkdir build
                cd build

           The default build (shared libraries, no debug, only the library)
           is made with
                cmake ..
           For other options, you can use these flags on the cmake line:
           * To make a static library:
                cmake .. -DBUILD_SHARED_LIBS=OFF
                make
           * To make a dynamic library (default) and STATIC (or builtin) dependencies:
                cmake .. -DSW_BUILD_SHARED_LIBS=0
                make
           * To build with debug:
                cmake .. -DCMAKE_BUILD_TYPE=Debug
                make
           * To make both the library and the programs:
                cmake .. -DBUILD_PROG=1
                make

           The programs are put in build/bin/
           To run these (e.g., for testing), move them to the prog
           directory and run them from there:
              cd bin
              mv * ../../prog/
              cd ../../prog
              alltests_reg generate
              alltests_reg compare

           To build the library directly from the root directory instead of
           the build subdirectory:
              mkdir build
              cmake -H . -Bbuild   (-H means the source directory,
                                    -B means the directory for the build
              make

    3. Building on Windows

       (a) Building with Visual Studio

           1. Download the latest SW
                  (Software Network https://software-network.org/)
              client from https://software-network.org/client/
           2. Unpack it, add to PATH.
           3. Run once to perform cmake integration:
              sw setup
           4. Run:
              git clone https://github.com/danbloomberg/leptonica
              cd leptonica
              mkdir build
              cd build
              cmake ..
           5. Build a solution (leptonica.sin) in your Visual Studio version.

       (b) Building for mingw32 with MSYS
           (Thanks to David Bryan)

           MSYS is a Unix-compatible build environment for the Windows-native
           mingw32 compiler.  Selecting the "mingw-developer-toolkit",
           "mingw32-base", and "msys-base" packages during installation will allow
           building the library with autoconf as in (2) above.  It will also allow
           building with the static makefile as in (1) above if this option is used
           in the make command line:

             CC='gcc -std=c99 -U__STRICT_ANSI__'

           Only the static library may be built this way; the autoconf method must
           be used if a shared (DLL) library is desired.

           External image libraries (see below) must be downloaded separately,
           built, and installed before building the library.  Pre-built libraries
           are available from the ezwinports project.

       (c) Building for Cygwin
           (Thanks to David Bryan)

           Cygwin is a Unix-compatible build and runtime environment.  Adding the
           "binutils", "gcc-core", and "make" packages from the "Devel" category and
           the "diffutils" package from the "Utils" category to the packages
           installed by default will allow building the library with autoconf as in
           (2) above.  Pre-built external image libraries are available in the
           "Graphics" and "Libs" categories and may be selected for installation.
           If the libraries are not installed into the /lib, /usr/lib, or
           /usr/local/lib directories, you must run make with the
           "LDFLAGS=-L/(path-to-image)/lib" option.  Building may also be performed
           with the static makefile as in (1) above if this option is used in the
           make command:

             CC='gcc -std=c99 -U__STRICT_ANSI__'

           Only the static library may be built this way; the autoconf method must
           be used if a shared (DLL) library is desired.

    4. Building and running oss-fuzz programs

       The oss-fuzz programs are in prog/fuzzing/.  They are run by oss-fuzz
       on a continual basis with random inputs.  clang-10, which is required
       to build these programs, can be installed using the command
           sudo apt-get install clang-10

       Stefan Weil has provided this method for building the fuzzing programs.
       From your github root:
           ./autogen.sh    (to make configure)
           mkdir -p bin/fuzzer
           cd bin/fuzzer
       Run configure to generate the Makefiles:
         address sanitizer issue:
           ../../configure CC=clang-10 CXX=clang++-10 CFLAGS="-g -O2 \
           -D_GLIBCXX_DEBUG -fsanitize=fuzzer-no-link,address,undefined" \
           CXXFLAGS="-g -O2 -D_GLIBCXX_DEBUG \
           -fsanitize=fuzzer-no-link,address,undefined"
         memory sanitizer issue:
           ../../configure CC=clang-10 CXX=clang++-10 CFLAGS="-g -O2 \
           -D_GLIBCXX_DEBUG -fsanitize=fuzzer-no-link,memory,undefined" \
           CXXFLAGS="-g -O2 -D_GLIBCXX_DEBUG \
           -fsanitize=fuzzer-no-link,memory,undefined"
       Build:
         address sanitizer issue:
           make fuzzers CXX=clang++-10 CXXFLAGS="-g -O2 -D_GLIBCXX_DEBUG \
           -fsanitize=fuzzer,address,undefined"
         memory sanitizer issue:
           make fuzzers CXX=clang++-10 CXXFLAGS="-g -O2 -D_GLIBCXX_DEBUG \
           -fsanitize=fuzzer,memory,undefined"

       When an oss-fuzz issue has been created, download the Reproducer
       Testcase file (e.g, name it "/tmp/payload").  To run one of the
       fuzzing executables in bin/fuzzer, e.g., pix4_fuzzer:
           cd ../../prog/fuzzing
           ../../bin/fuzzer/pix4_fuzzer /tmp/payload

    5. The 270+ programs in the prog directory are an integral part of this
       package.  They can be divided into four groups:

       (1) Programs that are useful applications for running on the
           command line.  They can be installed from autoconf builds
           using 'make install'.  Examples of these are the PostScript
           and pdf conversion programs: converttopdf, converttops,
           convertfilestopdf, convertfilestops, convertsegfilestopdf,
           convertsegfilestops, imagetops, printimage and printsplitimage.

       (2) Programs that are used as regression tests in alltests_reg.
           These are named *_reg, and 100 of them are invoked together
           (alltests_reg).  The regression test framework has been
           standardized, and regresstion tests are relatively easy
           to write.  See regutils.h for details.

       (3) Other regression tests, some of which have not (yet) been
           put into the framework.  They are also named *_reg.

       (4) Programs that were used to test library functions or auto-generate
           library code.  These are useful for testing the behavior of small
           sets of functions and for providing example code.

    6. Sanitizers can be used on all the regression tests in alltests_reg.c.

       First run autogen.sh to generate the configure script
         autogen.sh
       Then run configure to generate the Makefile with the address sanitizer
         ./configure '--disable-shared' '--enable-debug' 'CFLAGS=-D_GLIBCXX_DEBUG -DDEBUG=1 -Wall -pedantic -g -O0 -fsanitize=address,undefined -fstack-protector-strong -ftrapv'
       Make and run all the regression tests
          make check

## I/O libraries leptonica is dependent on

       Leptonica is configured to handle image I/O using these external
       libraries: libjpeg, libtiff, libpng, libz, libwebp, libgif, libopenjp2

       These libraries are easy to obtain.  For example, using the
       Debian package manager:
           sudo apt-get install
       where  = {libpng-dev, libjpeg62-turbo-dev, libtiff5-dev,
                          libwebp-dev, libopenjp2-7-dev, libgif-dev}.

       Leptonica also allows image I/O with bmp and pnm formats, for which
       we provide the serializers (encoders and decoders).  It also
       gives output drivers for wrapping images in PostScript and PDF, which
       in turn use tiffg4, jpeg and flate (i.e., zlib) encoding.  PDF will
       also wrap jpeg2000 images.

       There is a programmatic interface to gnuplot.  To use it, you
       need only the gnuplot executable (suggest version 3.7.2 or later);
       the gnuplot library is not required.

       If you build with automake, libraries on your system will be
       automatically found and used.

       The rest of this section is for building with the static makefiles.
       The entries in environ.h specify which of these libraries to use.
       The default is to link to these four libraries:
          libjpeg.a  (standard jfif jpeg library, version 6b or 7, 8 or 9))
          libtiff.a  (standard Leffler tiff library, version 3.7.4 or later;
          libpng.a   (standard png library, suggest version 1.4.0 or later)
          libz.a     (standard gzip library, suggest version 1.2.3)
                      current non-beta version is 3.8.2)

       These libraries (and their shared versions) should be in /usr/lib.
       (If they're not, you can change the LDFLAGS variable in the makefile.)
       Additionally, for compilation, the following header files are
       assumed to be in /usr/include:
          jpeg:  jconfig.h
          png:   png.h, pngconf.h
          tiff:  tiff.h, tiffio.h

       If for some reason you do not want to link to specific libraries,
       even if you have them, stub files are included for the ten
       different output formats:
            bmp, jpeg, png, pnm, ps, pdf, tiff, gif, webp and jp2.
       For example, if you don't want to include the tiff library,
       in environ.h set:
           #define  HAVE_LIBTIFF   0
       and the stubs will be linked in.

       To read and write webp files:
          (1) Download libwebp from sourceforge
          (2) #define HAVE_LIBWEBP   1  (in environ.h)
          (3) In prog/makefile, edit ALL_LIBS to include -lwebp
          (4) The library will be installed into /usr/local/lib.
              You may need to add that directory to LDFLAGS; or, equivalently,
              add that path to the LD_LIBRARY_PATH environment variable.

       To read and write jpeg2000 files:
          (1) Download libopenjp2, version 2.3, from their distribution.
          (2) #define HAVE_LIBJP2K   1  (in environ.h)
          (2a) If you have version 2.X, X != 3, edit LIBJP2K_HEADER  (in environ.h)
          (3) In prog/makefile, edit ALL_LIBS to include -lopenjp2
          (4) The library will be installed into /usr/local/lib.

       To read and write gif files:
          (1) Download version giflib-5.1.X+ from souceforge
          (2) #define  HAVE_LIBGIF   1  (in environ.h)
          (3) In prog/makefile, edit ALL_LIBS to include -lgif
          (4) The library will be installed into /usr/local/lib.

## Generating documentation using doxygen

    The source code is set up to allow generation of documentation using doxygen.
    To do this:
    (1) Download the Debian doxygen package:
         sudo apt-get install doxygen
    (2) In the root client directory containing Doxyfile:
         doxygen Doxyfile
    The documentation will be generated in a 'doc' subdirectory, accessible
    from this file (relative to the root)
        ./doc/html/index.html

## Developing with leptonica

    You are encouraged to use the static makefiles if you are developing
    applications using leptonica.  The following instructions assume
    that you are using the static makefiles and customizing environ.h.

    1. Automatic generation of prototypes

       The prototypes are automatically generated by the program xtractprotos.
       They can either be put in-line into allheaders.h, or they can be
       written to a file leptprotos.h, which is #included in allheaders.h.
       Note: (1) We supply the former version of allheaders.h.
             (2) all .c files simply include allheaders.h.

       First, make xtractprotos:
           make xtractprotos

       Then to generate the prototypes and make allheaders.h, do one of
       these two things:
           make allheaders  [puts everything into allheaders.h]
           make allprotos   [generates a file leptprotos.h containing the
                             function prototypes, and includes it in allheaders.h]

       Things to note about xtractprotos, assuming that you are developing
       in Leptonica and need to regenerate the prototypes in allheaders.h:

         (1) xtractprotos is part of Leptonica.  You can 'make' it in either
             src or prog (see the makefile).
         (2) You can output the prototypes for any C file to stdout by running:
                 xtractprotos      or
                 xtractprotos -prestring=[string]
         (3) The source for xtractprotos has been packaged up into a tar
             containing just the Leptonica files necessary for building it
             in Linux.  The tar file is available at:
                 www.leptonica.com/source/xtractlib-1.5.tar.gz

    2. Global parameter to enable development and testing

       For security reasons, with the exception of the regression utility
       (regutils.c), leptonica as shipped (starting with 1.77) does not allow:
          * 'system(3)' fork/exec
          * writes to temp files with compiled-in names
       System calls are used either to run gnuplot or display an image on
       the screen.

       This is enforced with a global parameter, LeptDebugOK, initialized to 0.
       It can be overridden either at compile time by changing the initialization
       (in writefile.c), or at runtime, using setLeptDebugOK().
       The programs in the prog directory, which mostly test functions in
       the library, are not subject to this restriction.

    3. GNU runtime functions for stream redirection to memory

       There are two non-standard gnu functions, fmemopen() and open_memstream(),
       that only work on Linux and conveniently allow memory I/O with a file
       stream interface.  This is convenient for compressing and decompressing
       image data to memory rather than to file.  Stubs are provided
       for all these I/O functions.  Default is to enable them; OSX developers
       must disable by setting #define HAVE_FMEMOPEN  0  (in environ.h).
       If these functions are not enabled, raster to compressed data in
       memory is accomplished safely but through a temporary file.
       See 9 for more details on image I/O formats.

       If you're building with the autoconf programs, these two functions are
       automatically enabled if available.

    4. Runtime functions not available on all platforms

       Some functions are not available on all systems.  One example of such a
       function is fstatat().  If possible, such functions will be replaced by
       wrappers, stubs or behavioral equivalent functions.  By default, such
       functions are disabled; enable them by setting #define HAVE_FUNC  1 (in
       environ.h).

       If you're building with the autoconf or cmake programs, these functions are
       automatically enabled if available.

    5. Typedefs

       A deficiency of C is that no standard has been universally
       adopted for typedefs of the built-in types.  As a result,
       typedef conflicts are common, and cause no end of havoc when
       you try to link different libraries.  If you're lucky, you
       can find an order in which the libraries can be linked
       to avoid these conflicts, but the state of affairs is aggravating.

       The most common typedefs use lower case variables: uint8, int8, ...
       The png library avoids typedef conflicts by altruistically
       appending "png_" to the type names.  Following that approach,
       Leptonica appends "l_" to the type name.  This should avoid
       just about all conflicts.  In the highly unlikely event that it doesn't,
       here's a simple way to change the type declarations throughout
       the Leptonica code:
        (1) customize a file "converttypes.sed" with the following lines:
            /l_uint8/s//YOUR_UINT8_NAME/g
            /l_int8/s//YOUR_INT8_NAME/g
            /l_uint16/s//YOUR_UINT16_NAME/g
            /l_int16/s//YOUR_INT16_NAME/g
            /l_uint32/s//YOUR_UINT32_NAME/g
            /l_int32/s//YOUR_INT32_NAME/g
            /l_float32/s//YOUR_FLOAT32_NAME/g
            /l_float64/s//YOUR_FLOAT64_NAME/g
        (2) in the src and prog directories:
           - if you have a version of sed that does in-place conversion:
                sed -i -f converttypes.sed *
           - else, do something like (in csh)
               foreach file (*)
               sed -f converttypes.sed $file > tempdir/$file
               end

       If you are using Leptonica with a large code base that typedefs the
       built-in types differently from Leptonica, just edit the typedefs
       in environ.h.  This should have no side-effects with other libraries,
       and no issues should arise with the location in which liblept is
       included.

       For compatibility with 64 bit hardware and compilers, where
       necessary we use the typedefs in stdint.h to specify the pointer
       size (either 4 or 8 byte).

    6. Compile and runtime control over stderr output (see environ.h and utils1.c)

       Leptonica provides both compile-time and run-time control over
       messages and debug output (thanks to Dave Bryan).  Both compile-time
       and run-time severity thresholds can be set.  The runtime threshold
       can also be set by an environmental variable.  Messages are
       vararg-formatted and of 3 types: error, warning, informational.
       These are all macros, and can be further suppressed when
       NO_CONSOLE_IO is defined on the compile line.  For production code
       where no output is to go to stderr, compile with -DNO_CONSOLE_IO.

       Runtime redirection of stderr output is also possible, using a
       callback mechanism.  The callback function is registered using
       leptSetStderrHandler().   See utils1.c for details.

    7. In-memory raster format (Pix)

       Unlike many other open source packages, Leptonica uses packed
       data for images with all bit/pixel (bpp) depths, allowing us
       to process pixels in parallel.  For example, rasterops works
       on all depths with 32-bit parallel operations throughout.
       Leptonica is also explicitly configured to work on both little-endian
       and big-endian hardware.  RGB image pixels are always stored
       in 32-bit words, and a few special functions are provided for
       scaling and rotation of RGB images that have been optimized by
       making explicit assumptions about the location of the R, G and B
       components in the 32-bit pixel.  In such cases, the restriction
       is documented in the function header.  The in-memory data structure
       used throughout Leptonica to hold the packed data is a Pix,
       which is defined and documented in pix.h.  The alpha component
       in RGB images is significantly better supported, starting in 1.70.

       Additionally, a FPix is provided for handling 2D arrays of floats,
       and a DPix is provided for 2D arrays of doubles.  Converters
       between these and the Pix are given.

    8. Conversion between Pix and other in-memory raster formats

     . If you use Leptonica with other imaging libraries, you will need
       functions to convert between the Pix and other image data
       structures.  To make a Pix from other image data structures, you
       will need to understand pixel packing, pixel padding, component
       ordering and byte ordering on raster lines.  See the file pix.h
       for the specification of image data in the pix.

    9. Custom memory management

       Leptonica allows you to use custom memory management (allocator,
       deallocator).  For Pix, which tend to be large, the alloc/dealloc
       functions can be set programmatically.  For all other structs and arrays,
       the allocators are specified in environ.h.  Default functions
       are malloc and free.  We have also provided a sample custom
       allocator/deallocator for Pix, in pixalloc.c.

## What's in leptonica?

    1. Rasterops

       This is a source for a clean, fast implementation of rasterops.
       You can find details starting at the Leptonica home page,
       and also by looking directly at the source code.
       Some of the low-level code is in roplow.c, and an interface is
       given in rop.c to the simple Pix image data structure.

    2. Binary morphology

       This is a source for efficient implementations of binary morphology
       Details are found starting at the Leptonica home page, and by reading
       the source code.

       Binary morphology is implemented two ways:

         (a) Successive full image rasterops for arbitrary
             structuring elements (Sels)

         (b) Destination word accumulation (dwa) for specific Sels.
             This code is automatically generated.  See, for example,
             the code in fmorphgen.1.c and fmorphgenlow.1.c.
             These files were generated by running the program
             prog/fmorphautogen.c. Results can be checked by comparing dwa
             and full image rasterops; e.g., prog/fmorphauto_reg.c.

       Method (b) is considerably faster than (a), which is the
       reason we've gone to the effort of supporting the use
       of this method for all Sels.  We also support two different
       boundary conditions for erosion.

       Similarly, dwa code for the general hit-miss transform can
       be auto-generated from an array of hit-miss Sels.
       When prog/fhmtautogen.c is compiled and run, it generates
       the dwa C code in fhmtgen.1.c and fhmtgenlow.1.c.  These
       files can then be compiled into the libraries or into other programs.
       Results can be checked by comparing dwa and rasterop results;
       e.g., prog/fhmtauto_reg.c

       Several functions with simple parsers are provided to execute a
       sequence of morphological operations (plus binary rank reduction
       and replicative expansion).  See morphseq.c.

       The structuring element is represented by a simple Sel data structure
       defined in morph.h.  We provide (at least) seven ways to generate
       Sels in sel1.c, and several simple methods to generate hit-miss
       Sels for pattern finding in selgen.c.

       In use, the most common morphological Sels are separable bricks,
       of dimension n x m (where either n or m, but not both, is commonly 1).
       Accordingly, we provide separable morphological operations on brick
       Sels, using for binary both rasterops and dwa.  Parsers are provided
       for a sequence of separable binary (rasterop and dwa) and grayscale
       brick morphological operations, in morphseq.c.  The main
       advantage in using the parsers is that you don't have to create
       and destroy Sels, or do any of the intermediate image bookkeeping.

       We also give composable separable brick functions for binary images,
       for both rasterop and dwa.  These decompose each of the linear
       operations into a sequence of two operations at different scales,
       reducing the operation count to a sum of decomposition factors,
       rather than the (un-decomposed) product of factors.
       As always, parsers are provided for a sequence of such operations.

    3. Grayscale morphology and rank order filters

       We give an efficient implementation of grayscale morphology for brick
       Sels.  See the Leptonica home page and the source code.

       Brick Sels are separable into linear horizontal and vertical elements.
       We use the van Herk/Gil-Werman algorithm, that performs the calculations
       in a time that is independent of the size of the Sels.  Implementations
       of tophat and hdome are also given.

       We also provide grayscale rank order filters for brick filters.
       The rank order filter is a generalization of grayscale morphology,
       that selects the rank-valued pixel (rather than the min or max).
       A color rank order filter applies the grayscale rank operation
       independently to each of the (r,g,b) components.

    4. Image scaling

       Leptonica provides many simple and relatively efficient
       implementations of image scaling.  Some of them are listed here;
       for the full set see the web page and the source code.

       Grayscale and color images are scaled using:
          - sampling
          - lowpass filtering followed by sampling,
          - area mapping
          - linear interpolation

       Scaling operations with antialiased sampling, area mapping,
       and linear interpolation are limited to 2, 4 and 8 bpp gray,
       24 bpp full RGB color, and 2, 4 and 8 bpp colormapped
       (bpp == bits/pixel).  Scaling operations with simple sampling
       can be done at 1, 2, 4, 8, 16 and 32 bpp.  Linear interpolation
       is slower but gives better results, especially for upsampling.
       For moderate downsampling, best results are obtained with area
       mapping scaling.  With very high downsampling, either area mapping
       or antialias sampling (lowpass filter followed by sampling) give
       good results.  Fast area map with power-of-2 reduction are also
       provided.  Optional sharpening after resampling is provided to
       improve appearance by reducing the visual effect of averaging
       across sharp boundaries.

       For fast analysis of grayscale and color images, it is useful to
       have integer subsampling combined with pixel depth reduction.
       RGB color images can thus be converted to low-resolution
       grayscale and binary images.

       For binary scaling, the dest pixel can be selected from the
       closest corresponding source pixel.  For the special case of
       power-of-2 binary reduction, low-pass rank-order filtering can be
       done in advance.  Isotropic integer expansion is done by pixel replication.

       We also provide 2x, 3x, 4x, 6x, 8x, and 16x scale-to-gray reduction
       on binary images, to produce high quality reduced grayscale images.
       These are integrated into a scale-to-gray function with arbitrary
       reduction.

       Conversely, we have special 2x and 4x scale-to-binary expansion
       on grayscale images, using linear interpolation on grayscale
       raster line buffers followed by either thresholding or dithering.

       There are also image depth converters that don't have scaling,
       such as unpacking operations from 1 bpp to grayscale, and
       thresholding and dithering operations from grayscale to 1, 2 and 4 bpp.

    5. Image shear and rotation (and affine, projective, ...)

       Image shear is implemented with both rasterops and linear interpolation.
       The rasterop implementation is faster and has no constraints on image
       depth.  We provide horizontal and vertical shearing about an
       arbitrary point (really, a line), both in-place and from source to dest.
       The interpolated shear is used on 8 bpp and 32 bpp images, and
       gives a smoother result.  Shear is used for the fastest implementations
       of rotation.

       There are three different types of general image rotators:

         a.  Grayscale rotation using area mapping
             - pixRotateAM() for 8 bit gray and 24 bit color, about center
             - pixRotateAMCorner() for 8 bit gray, about image UL corner
             - pixRotateAMColorFast() for faster 24 bit color, about center

         b.  Rotation of an image of arbitrary bit depth, using
             either 2 or 3 shears.  These rotations can be done
             about an arbitrary point, and they can be either
             from source to dest or in-place; e.g.
             - pixRotateShear()
             - pixRotateShearIP()

         c.  Rotation by sampling.  This can be used on images of arbitrary
             depth, and done about an arbitrary point.  Colormaps are retained.

       The area mapping rotations are slower and more accurate, because each
       new pixel is composed using an average of four neighboring pixels
       in the original image; this is sometimes also also called "antialiasing".
       Very fast color area mapping rotation is provided.

       The shear rotations are much faster, and work on images of arbitrary
       pixel depth, but they just move pixels around without doing any averaging.
       The pixRotateShearIP() operates on the image in-place.

       We also provide orthogonal rotators (90, 180, 270 degree; left-right
       flip and top-bottom flip) for arbitrary image depth.
       And we provide implementations of affine, projective and bilinear
       transforms, with both sampling (for speed) and interpolation
       (for antialiasing).

    6. Sequential algorithms

       We provide a number of fast sequential algorithms, including
       binary and grayscale seedfill, and the distance function for
       a binary image.  The most efficient binary seedfill is
       pixSeedfill(), which uses Luc Vincent's algorithm to iterate
       raster- and antiraster-ordered propagation, and can be used
       for either 4- or 8-connected fills.  Similar raster/antiraster
       sequential algorithms are used to generate a distance map from
       a binary image, and for grayscale seedfill.  We also use Heckbert's
       stack-based filling algorithm for identifying 4- and 8-connected
       components in a binary image.  A fast implementation of the
       watershed transform, using a priority queue, is included.

    7. Image enhancement

       Some simple image enhancement routines for grayscale and color
       images have been provided.  These include intensity mapping with
       gamma correction and contrast enhancement, histogram equalization,
       edge sharpening, smoothing, and various color-shifting operations.

    8. Convolution and cousins

       A number of standard image processing operations are also
       included, such as block convolution, binary block rank filtering,
       grayscale and rgb rank order filtering, and edge and local
       minimum/maximum extraction.   Generic convolution is included,
       for both separable and non-separable kernels, using float arrays
       in the Pix.  Two implementations are included for grayscale and
       color bilateral filtering: a straightforward (slow) one, and a
       fast, approximate, separable one.

    9. Image I/O

       Some facilities have been provided for image input and output.
       This is of course required to build executables that handle images,
       and many examples of such programs, most of which are for
       testing, can be built in the prog directory.  Functions have been
       provided to allow reading and writing of files in JPEG, PNG,
       TIFF, BMP, PNM ,GIF, WEBP and JP2 formats.  These formats were chosen
       for the following reasons:

        - JFIF JPEG is the standard method for lossy compression
          of grayscale and color images.  It is supported natively
          in all browsers, and uses a good open source compression
          library.  Decompression is supported by the rasterizers
          in PS and PDF, for level 2 and above.  It has a progressive
          mode that compresses about 10% better than standard, but
          is considerably slower to decompress.  See jpegio.c.

        - PNG is the standard method for lossless compression
          of binary, grayscale and color images.  It is supported
          natively in all browsers, and uses a good open source
          compression library (zlib).  It is superior in almost every
          respect to GIF (which, until recently, contained proprietary
          LZW compression).  See pngio.c.

        - TIFF is a common interchange format, which supports different
          depths, colormaps, etc., and also has a relatively good and
          widely used binary compression format (CCITT Group 4).
          Decompression of G4 is supported by rasterizers in PS and PDF,
          level 2 and above.  G4 compresses better than PNG for most
          text and line art images, but it does quite poorly for halftones.
          It has good and stable support by Leffler's open source library,
          which is clean and small.  Tiff also supports multipage
          images through a directory structure.  Note: because jpeg is
          a supported tiff compression mode, leptonica requires linking
          both libtiff and libjpeg to read and write tiff.  See tiffio.c

        - BMP has (until recently) had no compression.  It is a simple
          format with colormaps that requires no external libraries.
          It is commonly used because it is a Microsoft standard,
          but has little besides simplicity to recommend it.  See bmpio.c.

        - PNM is a very simple, old format that still has surprisingly
          wide use in the image processing community.  It does not
          support compression or colormaps, but it does support binary,
          grayscale and rgb images.  Like BMP, the implementation
          is simple and requires no external libraries.  See pnmio.c.

        - WEBP is a new wavelet encoding method derived from libvpx,
          a video compression library.  It is rapidly growing in acceptance,
          and is supported natively in several browsers.  Leptonica provides
          an interface through webp into the underlying codec.  You need
          to download libwebp.  See webpio.c.

        - JP2 (jpeg2000) is a wavelet encoding method, that has clear
          advantages over jpeg in compression and quality (especially when
          the image has sharp edges, such as scanned documents), but is
          only slowly growing in acceptance.  For it to be widely supported,
          it will require support on a major browser (as with webp).
          Leptonica provides an interface through openjpeg into the underlying
          codec.  You need to download libopenjp2, version 2.X.  See jp2kio.c.

        - GIF is still widely used in the world.  With the expiration
          of the LZW patent, it is practical to add support for GIF files.
          The open source gif library is relatively incomplete and
          unsupported (because of the Sperry-Rand-Burroughs-Univac
          patent history).  Leptonica supports versions 5.1+.  See gifio.c.

       Here's a summary of compression support and limitations:
          - All formats except JPEG, WEBP and JP2K support 1 bpp binary.
          - All formats support 8 bpp grayscale (GIF must have a colormap).
          - All formats except GIF support rgb color.
          - All formats except PNM, JPEG, WEBP and JP2K support 8 bpp colormap.
          - PNG and PNM support 2 and 4 bpp images.
          - PNG supports 2 and 4 bpp colormap, and 16 bpp without colormap.
          - PNG, JPEG, TIFF, WEBP, JP2K and GIF support image compression;
            PNM and BMP do not.
          - WEBP supports rgb color and rgba.
          - JP2 supports 8 bpp grayscale, rgb color and rgba.
       Use prog/ioformats_reg for a regression test on all formats, including
       thorough testing on TIFF.
       For more thorough testing on other formats, use:
          - prog/pngio_reg for PNG.
          - prog/gifio_reg for GIF
          - prog/webpio_reg for WEBP
          - prog/jp2kio_reg for JP2

       We provide generators for PS output, from all types of input images.
       The output can be either uncompressed or compressed with level 2
       (ccittg4 or dct) or level 3 (flate) encoding.  You have flexibility
       for scaling and placing of images, and for printing at different
       resolutions.  You can also compose mixed raster (text, image) PS.
       See psio1.c for examples of how to output PS for different applications.
       As examples of usage, see:
         * prog/converttops.c for a general image --> PS conversion
               for printing.  You can specify the PS compression level (1, 2, or 3).
         * prog/imagetops.c for a special image --> PS conversion
               for printing at maximum size on 8.5 x 11 paper.  You can
               specify the PS compression level (1, 2, or 3).
         * prog/convertfilestops.c to generate a multipage level 3 compressed
               PS file that can then be converted to pdf with ps2pdf.
         * prog/convertsegfilestops.c to generate a multipage, mixed raster,
               level 2 compressed PS file.

       We provide generators for PDF output, again from all types of input
       images, and with ccittg4, dct, flate and jpx (jpeg2000) compression.
       You can do the following for PDF:
         * Put any number of images onto a page, with specified input
           resolution, location and compression.
         * Write a mixed raster PDF, given an input image and a segmentation
           mask.  Non-image regions are written in G4 (fax) encoding.
         * Concatenate single-page PDF wrapped images into a single PDF file.
         * Build a PDF file of all images in a directory or array of file names.
       As examples of usage, see:
         * prog/converttopdf.c: fast pdf generation with one image/page.
           For speed, this avoids transcoding whenever possible.
         * prog/convertfilestopdf.c: more flexibility in the output.  You
           can set the resolution, scaling, encoding type and jpeg quality.
         * prog/convertsegfilestopdf.c: generates a multipage, mixed raster pdf,
           with separate controls for compressing text and non-text regions.

       Note: any or all of these I/O library calls can be stubbed out at
             compile time, using the environment variables in environ.h.

       For all formatted reads and writes, we support read from memory
       and write to memory.  The gnu C runtime library (glibc) supports
       two I/O functions, open_memstream() and fmemopen(), which read
       and write directly to memory as if writing to a file stream.
         * On all platforms, leptonica supports direct read/write with memory
           for TIFF, PNG, BMP, GIF and WEBP formats.
         * On linux, leptonica uses the special gnu libraries to enable
           direct read/write with memory for JPEG, PNM and JP2.
         * On platforms without the gnu libraries, such as OSX, Windows
           and Solaris, read/write with memory for JPEG, PNM and JP2 goes
           through temp files.
       To enable/disable memory I/O for image read/write, see environ.h.

       We also provide fast serialization and deserialization between a pix
       in memory and a file (spixio.c).  This works on all types of pix images.

    10. Colormap removal and color quantization

       Leptonica provides functions that remove colormaps, for conversion
       to either 8 bpp gray or 24 bpp RGB.  It also provides the inverse
       function to colormap removal; namely, color quantization
       from 24 bpp full color to 8 bpp colormap with some number
       of colormap colors.  Several versions are provided, some that
       use a fast octree vector quantizer and others that use
       a variation of the median cut quantizer.  For high-level interfaces,
       see for example: pixConvertRGBToColormap(), pixOctreeColorQuant(),
       pixOctreeQuantByPopulation(), pixFixedOctcubeQuant256(),
       and pixMedianCutQuant().

    11. Programmatic image display

       For debugging, pixDisplay() and pixDisplayWithTitle() in writefile.c
       can be called to display an image using one of several display
       programs (xzgv, xli, xv, l_view).  If necessary to fit on the screen,
       the image is reduced in size, with 1 bpp images being converted
       to grayscale for readability.  Another common debug method is to
       accumulate intermediate images in a pixa, and then either view these
       as a mosaic (using functions in pixafunc2.c), or gather them into
       a compressed PDF or PostScript file for viewing with evince.  Common
       image display programs are: xzgv, xli, xv, display, gthumb, gqview,
       evince, gv and acroread.

    12. Document image analysis

       Many functions have been included specifically to help with
       document image analysis.  These include skew and text orientation
       detection; page segmentation; baseline finding for text;
       unsupervised classification of connected components, characters
       and words; dewarping camera images; adaptive binarization; and
       a simple book-adaptive classifier for various character sets,
       segmentation for newspaper articles, etc.

    13. Data structures

       Several simple data structures are provided for safe and efficient handling
       of arrays of numbers, strings, pointers, and bytes.  The generic
       pointer array is implemented in four ways: as a stack, a queue,
       a heap (used to implement a priority queue), and an array with
       insertion and deletion, from which the stack operations form a subset.
       Byte arrays are implemented both as a wrapper around the actual
       array and as a queue.  The string arrays are particularly useful
       for both parsing and composing text.  Generic lists with
       doubly-linked cons cells are also provided.  Other data structures
       are provided for handling ordered sets and maps, as well as hash sets
       and hash maps.

    14. Examples of programs that are easily built using the library:

        - for plotting x-y data, we give a programmatic interface
          to the gnuplot program, with output to X11, png, ps or eps.
          We also allow serialization of the plot data, in a form
          such that the data can be read, the commands generated,
          and (finally) the plot constructed by running gnuplot.

        - a simple jbig2-type classifier, using various distance
          metrics between image components (correlation, rank
          hausdorff); see prog/jbcorrelation.c, prog/jbrankhaus.c.

        - a simple color segmenter, giving a smoothed image
          with a small number of the most significant colors.

        - a program for converting all images in a directory
          to a PostScript file, and a program for printing an image
          in any (supported) format to a PostScript printer.

        - various programs for generating pdf files from compressed
          images, including very fast ones that don't scale and
          avoid transcoding if possible.

        - converters between binary images and SVG format.

        - an adaptive recognition utility for training and identifying
          text characters in a multipage document such as a book.

        - a bitmap font facility that allows painting text onto
          images.  We currently support one font in several sizes.
          The font images and postscript programs for generating
          them are stored in prog/fonts/, and also as compiled strings
          in bmfdata.h.

        - a binary maze game lets you generate mazes and find shortest
          paths between two arbitrary points, if such a path exists.
          You can also compute the "shortest" (i.e., least cost) path
          between points on a grayscale image.

        - a 1D barcode reader.  This is still in an early stage of development,
          with little testing, and it only decodes 6 formats.

        - a utility that will dewarp images of text that were captured
          with a camera at close range.

        - a sudoku solver and generator, including a good test for uniqueness

        - see (13, above) for other document image applications.

    15. JBig2 encoder

       Leptonica supports an open source jbig2 encoder (yes, there is one!),
       which can be downloaded from:
           http://www.imperialviolet.org/jbig2.html.
       To build the encoder, use the most recent version.  This bundles
       Leptonica 1.63.  Once you've built the encoder, use it to compress
       a set of input image files:  (e.g.)
           ./jbig2 -v -s   >
       You can also generate a pdf wrapping for the output jbig2.  To do that,
       call jbig2 with the -p arg, which generates a symbol file (output.sym)
       plus a set of location files for each input image (output.0000, ...):
            ./jbig2 -v -s -p
       and then generate the pdf:
           python pdf.py output  >
       See the usage documentation for the jbig2 compressor at:
           http://www.imperialviolet.org/binary/jbig2enc.html
       You can uncompress the jbig2 files using jbig2dec, which can be
       downloaded and built from:
           http://jbig2dec.sourceforge.net/

    16. Versions

       New versions of the Leptonica library are released several times
       a year, and version numbers are provided for each release in the
       following files:
           src/makefile.static
           CMakeLists.txt
           configure.ac
           allheaders_top.txt  (and propagated to allheaders.h)
       All even versions from 1.42 to 1.60 were originally archived at
       http://code.google.com/p/leptonica, as well as all versions after 1.60.
       These have now been transferred by Egor Pugin to github:
           github.com/danbloomberg/leptonica
       where all releases (1.42 - 1.84.0) are available; e.g.,
           https://github.com/DanBloomberg/leptonica/releases/tag/1.84.0
       The more recent releases, from 1.80, are also available at
           leptonica.org/download.html
       Note that if you are downloading from github, the releases are more
       likely to be stable than the master.  Also, if you download from
       the master and use autotools (e.g., Makefile.am), you must first run
       autogen.sh to generate the configure program and the Makefiles.

       The number of downloads of leptonica increased by nearly an order
       of magnitude with 1.69, due to bundling with tesseract and
       incorporation in ubuntu 12-04.  Jeff Breidenbach has built all
       the Debian releases, which require release version numbers.
       The Debian binary release versions to date are:
            1.69 : 3.0.0
            1.70 : 4.0.0
            1.71 : 4.2.0
            1.72 : 4.3.0
            1.73 : 5.0.0
            1.74 : 5.1.0
            1.75 : 5.2.0
            1.76 : 5.3.0
            1.77 : 5.3.0
            1.78 : 5.3.0
            1.79 : 5.4.0
            1.80 : 5.4.0
            1.81 : 5.4.0
            1.82 : 5.4.0
            1.83 : 6.0.0
            1.84 : 6.0.0

       A brief version chronology is maintained in version-notes.html.
       Starting with gcc 4.3.3, error warnings (-Werror) are given for
       minor infractions like not checking return values of built-in C
       functions.  I have attempted to eliminate these warnings.
       In any event, you will see warnings with the -Wall flag.